Radiocircuit



March 6, 1934. L L, JQNES 1,949,475

RADIOCIRCUIT Filed March 28, 1929 INVENTOR Lesi'er L. Jones g BY 5! ATTORNEYS Patented Mar. 6, 1934 RADIOCIROUIT Lester L. Jones, Gradell, N. J.

Application March 23,

32 Claims.

This invention relates to radio circuits and more particularly to radio receiving sets.

A popular reproducer used with radio receiving sets is the electro-dynamic speaker. This type of speaker employs a field winding through which uni-directional current is passed in order to create an intense and steady magnetic field in which an armature coil carrying the signal current is ibrated. To energize the field of the speaker requires a considerable amount of energy, the provision of which may not be possible with receivers not designed especially for use with this type of speaker. One primary object'of my invention resides in the economical and convenient provision of the necessary field energizing current, which object I fulfill, generally speaking, by separating a pulsating signal energy into its steady component and signal component, and utilizing the steady component for energizing the field of the reproducer.

While the foregoing invention may be applied in a number or" ways, some of which will be described more in detail later, I am more especially interested in its application to receiving circuits of a common type which employ an audio frequency power stage between the receiver itself the reproducer. The power stage is usually energized at a direct potential which is considerably higher than that needed to energize the amplifier tubes of the receiver. Inasmuch as it ordinarily is convenient to employ a single source of direct energy for the entire receiving system it then becomes necessary to reduce the voltage of the source before applying it to the anodes of the amplifier tubes. To obtain the desired reduced voltage and to simultaneously energize the field of he reproducer without wasting eneris another object of my invention, which I fulfill by feeding the anode current. from the source to the amplifier through the field coil of the r producer. In one aspect, this may be conas a method of providing a desired potential between a pair of electrodes of a tube, and at the same time energizing the field of the reproducer, by utilizing the steady component of the current flowing between the pair of electrodes for the field of the reproducer.

The practice of the foregoing method in receivers wherein the volume control is obtained by changing the sensitivity or amplification of receiver is accompanied by the disadvantage that the speaker field energization' varies with changes i sensitivity produced by the volume control. Thus, when r ceiving local stations the amplification is greatly reduced; and the anode 1929, Serial No. 350,730

current of the tubes is consequently out down to so small a value that the reproducer field is weakened enough to prevent the speaker from properly reproducing the signals even though the latter are transmitted from a nearby station. If it is attempted to increase the volume by partially restoring the sensitivity of the receiver a relatively great increase in sensitivity produces only a slight increase in the speaker field exr additional auxiliary current from the direct ourrent source through the reproducer field windings, and varying the magnitude of this auxiliary current in the opposite direction to the variation in sensitivity of the amplifier produced by the volume control, in order to keep up the field strength of the reproducer. More specifically, I prefer to more than compensate for the diminished amplifier current, so that while varying the sensitivity of the amplifier I simultaneously and oppositely vary the strength of field energization of the reproducer.

The sensitivity of the amplifier may be varied by varying the magnitude of the direct potential applied to the anodes thereof. If this mode of variation is employed, a diificulty arises in connection with the bias on the control electrodes of the tubes. The anode voltage is apt to be most sharply reduced upon the reception of a local station, for when receiving under these conditions the signal voltage initially impressed on the control electrode or" even the first amplifier tube is large and is apt to exceed or over-run the bias of the amplifier tubes. Furthermore, modern receivers'are usually energized from a single power source, and the biasing voltage is derived from the flow of anode'ourrent through a resistance, and in such case the foregoing condition is aggravated because the drop in anode current, due to the reduction in anode voltage, causes a drop in the control electrode bias potential, just when such a change is least desired. A further object of the present invention, therefore, is to overcome this difiiculty, which I do by varying not only the magnitude of the direct anode potential, but also simultaneously and oppositely varying the magnitude of the control electrode bias potential. The resulting increased bias itself serves to operate in the proper direction upon the sensitivity of the amplifier, and also serves to prevent over-running of the bias potential when receiving a powerful locally transmitted signal.

It will thus be seen that my volume controlling method includes varying the anode potential of the amplifier, varying the control electrode bias potential of the amplifier, and varying the strength of field energization of the reproducer, and, with proper precautions, any desired combination of less than all of these three elements may be employed, as well as all three of them.

In a typical receiver the foregoing mode of energization of the reproducer field provides, say, 6 watts of energy. The field needed is so intense that ordinary speakers of this type dissipate, say, 12 watts of energy for field energization. It is quite possible to provide the necessary field by using an increased number of field turns, and so to operate the speaker on 6 watts of energy. However, the increase in size, weight, and cost of the speaker is so rapid when the available energy is decreased that it is exceedingly desirable to provide the 12 watts rather than the lesser amount of energy. The additional energy may be provided directly from the same or any other direct current source, and to make this reinforcement conveniently possible my invention includes the provision of a novel type of reproducer having a plurality of separate field coils in which currents of different magnitudes, supplied at difierent potentials may readily be utilized.

A still further object of my invention is to provide even the additional field energy by utilizing waste energy. Now, it is obvious that the power stage of the receiver draws a larger current sup ply from the direct current source than the other portions of the receiver, suchas the radio frequency amplifier. Neverthless, it is not desirable, in the ordinary case, to utilize this current for energizing the field of the reproducer because the full available direct potential should be applied to the anodes of the power tubes. In fact, the anode potential for the power stage is often taken from an intermediate filter stage, instead of from the final filter stage, in order to increase this potential. However, it is necessary to negatively bias the control electrodes of the power tubes, and this negative bias is larger in value. It heretofore has been obtained from the flow of the steady component of the anode current through a fixed resistance. In accordance with a further feature of my invention, I avoid the waste of the energy consumed in such a biasing resistance, and instead utilize this energy to fur,- ther excite the field of the reproducer. The anode current of the power stage is separated into its signal and steady components, and only thesteady component is employed in the speaker field. It is obvious that while a lower potential difierence is here available than in the case of the potential reduction applied between the direct current source and the radio frequency amplifier, the current is commensurately larger,

and an approximately similar quantity of energy, say 6 watts, is available in each case for energizing the speaker field. Of course, either type of field energization may be employed alone or, as I prefer, both may be employed together, and in the latter case the reproducer is equipped with a plurality of separate field coils. No claim is laid herein to the reproducer per se, for that is claimed in a copending divisional application, Serial No. 350,732, filed concurrently herewith.

To the accomplishment of the foregoing and such other objects as will hereinafter appear, my invention consists in the circuit elements and their relation one to the other, as hereinafter are more particularly described in the specification and sought to be defined in the claims. The specification is accompanied by a drawing in which:

Fig. l is a wiring diagram showing one application of one of the features of my invention; and

Fig. 2 is a wiring diagram for a broadcast receiver embodying further features of my invention.

The energization of the field of a reproducer having an externally energized field, such as an electro-dynamic speaker, presents considerable difficulty when the speaker is used with a receiver which is not provided with a source of direct energy for this purpose. Furthermore, even if such a source is available a further difficulty presents itself when the reproducer is to be used at a distance from the radio set, because instead of a simple two wire extension cord it is necessary to also extend other conductors for supplying the field current. To overcome either or both of the foregoing difiiculties I separate the pulsating receiver output current itself into its direct and alternating components, and use the former for exciting the field of the reproducer, and the latter for energizing the moving or armature coil thereof.

Such an arrangement is shown in Fig. 1, in which a receiver, indicated generally at A, is coupled to a near or remote reproducer, indicated generally at B, by a simple two-wire line C. At the receiver the line C is connected to the anode 2 of the final tube of the receiver and to the usual source of anode potential.

At the reproducer the line is connected to two parallel' circuits, one consisting of the field coil 4 of the reproducer, and the other comprising a condenser 6 and a transformer 8. The condenser 6 blocks the direct component of the pulsating anode current flowing through the line C, but is sufficiently large to readily pass the audio frequency component, which then is coupled through the transformer 8 to the movable coil or armature 10 of the reproducer. ary coil 4 is so large in inductance that it effectively blocks the alternating component of the signal energy, but meanwhile is traversed by the steady component thereof, which serves to create the desired magnetic field in the core 12. i The latter is preferably laminated in order to aid in the development of sumcient inductive reactance in the field coil to more effectively prevent the fiow of the speech component of the signal energy.

The stationy One advantage of this connection is that it automatically eliminates the probability of saturating the core of the transformer 8 used to supply energy to the armature coil 10, for the direct current component is not led through the by the omission of the transformer 8, although e its use is desirable in order to permit of the selection of the proper tube matching impedance, and further, to insulate the armature coil 10 from the relatively high anode potential applied to the final amplifier stage of the receiver.

Considered broadly, it will be perceived that in the foregoing arrangement the alternating and direct components of the current fiowing between a pair of electrodes of a tube have been separated, and the direct current component used for energizing the speaker field. The object in so doing was merely to obtain the desired field energization, and not to affect the potential difference between the electrodes. My invention may be applied with this further object in view, and preferable modes of application are illustrated in the receiver circuit shown in Fig. 2.

Referring thereto, there is a suitable antenna or signal collecting circuit D, the energy picked up by which is amplified in a radio frequency amplifier E, after which it is rectified in any suitable detector F in order to make available the audio frequency component thereof, which then may be amplified in an audio frequency amplifier here exemplified by a push-pull power stage G, the output from which is translated in an electro-dynamic reproducer H. The entire receiving system is energized from a source of direct energy generally indicated at J, the latter comprising a power line transformer K, a rectifier L, and a filter M. The details or" the radio frequency amplifier and detector, and the wiring for the filament heating currents of the tubes, have all been omitted in order to simplify the diagram.

The power stage G necessitates an anode voltage of the order of magnitude of 250 to volts and, consequently, the power source J is designed to supply this voltage. The tubes in the amplifier E need only be supplied with an anode voltage of the order of magnitude of 100 volts, and it has been customary heretofore to obtain the necessary reduction in voltage by dissipating energy in a fixed resistance. Now, in accordance with my invention, the anode current for the amplifier E is fed from the positive side 20 of the power source, by way of a lead 22, through the field coil 24 of the speaker H, and thence to the amplifier E.

The field coil of the dynamic speaker may be used as one of the chokes in the filter M, but this causes a hum in the speaker field which is a particularly deceptive one because it is not discernible when no signal is being received, inasmuch as the armature coil of the speaker is then carrying no current. In other words, the hum exists during reception and spoils the quality of reproduction and yet disappears during intervals of no reception, and, therefore, is difficult to discover. In the present arrangement the field is not energized until after the energy therefor has been completely smoothed by the action of the filter M, and meanwhile no extra energy is employed for the field, the voltage drop introduced by the field coil 24 being anyway necessary, and usually completely wasted in a resistor.

My invention also involves a novel and very efiective volume control for the receiver. The provision of a really satisfactory volume control in a radio receiver is exceedingly diificult. The range of volume control must be sufiiciently great to take care of the product of desired variations in loudness of output, and the unavoidable variations in radio signal field strength. Loudness variation should preferably range from,

say of a volt to volts on the speaker, or a range of 600. The available signal amplitude may range from 1 1G- to 2 volts, or a range of 2x10 The product gives a desired range of volume control of 1.2 l0 which is enormous, and practically impossible to accommodate by antenna shunt resistances of any commercially practicable type. Furthermore, such a volume control has the disadvantage of keeping up tube noises at maximum volume even when receiving a strong signal, for the signal is weakened, instead of the amplification being reduced.

I, therefore, prefer to obtain volume control by varying the sensitivity of the amplifier. However, this variation changes the magnitude of the anode current fiowing through the amplifier tubes, and with a circuit such as I have so far described, it therefore also changes the energization of the speaker. 011 superficial consideration, it might be supposed desirable to reduce the speaker field when reducing volume, but on more careful in vestigation l find that just the opposite result is preferable, for the reduction in field strengt produced when receiving a strong signal may necessitate so strong an armature coil input for the speaker that the receiver tubes, and par icularly the power stage tubes, are overloaded and introduce distortion in the speech wave form. Also, the efficient operation and faithful reproduction by the speaker requires that the field be kept up to strength, and preferably even increased, when the volume is low. If the amplifier sensitivity has been greatly reduced, as it is during the reception of a local station, the speaker field is unduly weakened, and any attempt to increase the output volume by partially restoring the sensitivity of amplifier only slightly increases the field excitation at a time when the last amplifier tubes may a.ready be overloaded. Differently expressed, the normal changes in speaker field energization and in amplification are not commensurately related for optimum results.

Another disadvantage resulting from the foregoing volume control system is that when the supply of current for the radio frequency amplifying tubes is greatly reduced the voltage supplied to the other units increases due to the normally poor inherent regulation of the power supply device. The rise in voltage also puts an undue load on other elements, such as the bypass condensers and filter condensers in the power box, thereby increasing the possibility of break-downs.

To overcome the foregoing difficulties I control volume by varying the sensitivity of the amplifier and simultaneously and oppositely varying the strength of field energization of the reproducer. For this purpose I provide a volume controlling resistance 26 connected from the anode supply lead of the amplifier E to the'negative side 30 of the source J. In other words, the volume control T;

circuit is an additional return circuit from the field coil as connected in parallel with the circuit from the anodes of the amplifier tubes to the negative side of the source J. To reduce the output volume the resistance 26 is reduced, and this This decreases the sensitivity field energization caused by the increased current flow through the volume control circuit. It may incidentally be mentioned that the compensating current taken through the volume control circuit results in a more nearly constant, or else increasing load on the direct current source J, and so improves the voltage regulation.

In connection with volume control it should be kept in mind that its most difiicult function is to take care of variations in the signal field strength to which the receiver must respond. The difference in field strength between a local and a distant station is much greater than the differences which the listener may wish to introduce in the ultimate acoustic output. To counteract these difierences in field strength the receiver should be capable of reducing the total radio frequency amplification of the receiver to zero, and furthermore should preferably be capable even of diminishing the output relative to the input when receiving a powerful local signal.

In the latter case, distortion may be introduced by the signal over-running the bias on the initial amplifier tubes. In the case of a signal of intermediate strength the bias of a later amplifier tube may be over-run. In power line operated receivers, such as that here disclosed, it is customary to derive the bias potential from the flow of anode current through a resistor, and with such an arrangement the tendency to overrun the bias of the tubes is aggravated by the reduction in anode current caused by the reduction in anode potential. In other words, a powerful local signal tends to over-run the control electrode bias potential, and meanwhile, the anode potential being greatly reduced in order to cut down the volume of reception, a decrease in bias potential is caused at a time when there preferably ought to be provided an increase in bias potential.

A further feature of my invention provides such an increase, and is next described. Referring to the drawing, a resistance 32 is arranged between the lead 34 coming from the cathodes of the amplifier tubes and the lead 36 running to the control electrodes of the amplifier tubes. The steady component of the anode to cathode current of the amplifier flows from the cathodes by way of lead 34 through resistance 32 and finally to the negative terminal 30 of the source J. The

resulting potential difference across the resistance 32 is the bias potential applied between the control electrodes and the cathodes of the amplifier tubes. Now, in accordance with the present invention, the volume control resistance 26 is connected in shunt with the anode to cathode circuit of the amplifier, rather than directly from the anode lead of the amplifier to the source J. In consequence, the resistance 32 is traversed not only by the anode to cathode current of the amplifier, but also by the current flowing through the volume control circuit. Differently expressed, all of the current passing through the field coil 24 also passes through the resistance 32, and it has already been explained that this current is increased when the sensitivity of the amplifier is decreased, and it therefore follows that the bias of the amplifier is increased when the anode potential is decreased.

It should be recognized that my novel volume control arrangement thus causes three simultaneous and desirably related changes, for the anode potential is varied, the speaker energization is varied, and the control electrode bias potential is varied. The anode potential variation may be usefully employed with the field variation, for reasons already set forth in detail. Similarly, if it is desired to employ control electrode bias variation alone for altering the sensitivity of the amplifier, this may be employed with the variation in reproducer field intensity, for identical reasons, though in passing I may state that I do not approve of this latter mode of volume control because it changes the effective tube resistance and therefore affects the stability, and the tendency to oscillate, of the amplifier. finally, regardless of what type of speaker is employed, and whether its field is or is not varied, the simultaneous and opposite variation in anode and control electrode potentials may itself be usefully and advantageously employed for controlling the sensitivity of an amplifier.

The volume control circuit is shown as including a fixed resistance 28. This is made of suitable magnitude, say 1000 to 2000 ohms, so that when the resistance 26, which may be, say 20,000 ohms, is reduced to zero, the current flow through the resistance 32, which may be, say ohms, will produce a sufficiently high negative bias potential to actually or very nearly secure cutofi in the amplifier tubes, which, of course, is equivalent to zero output. In this manner the full range of the variable resistance may be used for a maximum range of volume control, and the volume control obtained will be smooth and even in growth over this entire range. The resistance 28 may be omitted, but in such cases a portion of the variable resistance 26 will not be available for effective volume control, inasmuch as the And volume will be reduced to zero before the resistand therefore more gradually varied portion of the resistance is wasted if the external fixed resistance is not employed. Furthermore, the current flow through the volume control circuit is a maximum when its resistance is a minimum, H and it therefore follows that the heat dissipa- 1 tion is greatest when the resistance 26 is cut out of the circuit. In order to dissipate the excessive heat then generated, it is particularly desirable to have the resistance 28 in the form of an external resistor constructed and located with these conditions kept in view.

The magnitude of the external fixed resistance 28 may be determined as follows. Cut off of plate current in amplifying tubes occurs when the plate voltage is approximately equal to, or say 5 or 10 percent less than, the product of the biasing voltage and the amplification constant of the amplifier tubes. Knowing the desirable value of the biasing resistance, it follows that the fixed resistance should be slightly smaller than the product of the bias resistance times the amplification constant of the tubes being used. The current flow through these two resistances is identical at cutoff, for no anode current flows at that time.

It is customary in present receivers to employ electrode potentials on the detector tube which are quite different from those employed on the amplifier tubes. This condition may, if desired, be accommodated by the provision of a potentiometer resistance 40, at suitable tapping points on which leads are taken to the electrodes of the detector tube.

An electro-dynamic speaker requires an intense magnetic field. With a given amount of energy available, it is possible to design the field winding for the proper field strength. However, the number of turns and, consequently, the weight, the size, and the cost of the speaker increase enormously with a decrease in available power. A speaker designed to operate on 12 watts of field energy may be manufactured for about half the cost of a speaker designed to operate on, say 6 watts of field energy. In an average set the field energization obtained by the already described expedient is of the order of magnitude of say 6 watts. It is, therefore, desirable to augment the field energization, if possible, and, in accordance with another feature of my invention, I make this possible by the provision of an electro-dynamic speaker which is novel in having a plurality of field coils, instead of a single field coil, as has heretofore been the case. In this manner an additional field coil may be energized directly from the power box, as is indicated by the coil 41.

However, one of the prime objects of the present invention is to completely operate an electrodynamic speaker by the utilization of waste energy. It should be noted that the push-pull power stage G requires direct anode current in excess of that required by the radio frequency amplifier tubes, but it is not desirable to feed this current through a speaker field coil on its the power stage is frequently taken, as is indicated at 21 in the wiring diagram, from an intermediate tap on the filter M. This provides a higher potential, for the potential drop in the succeeding filter stages is avoided, and meanwhile, the tendency toward the production of a hum is counteracted by the fact that the power stage G is a push-pull stage, and anode current fluctuations, corresponding to any possible hum. fiow equally and oppositely in the two halves of the primary of the output transformer of the stage, and therefore are not coupled to the transformer secondary and the reproducer.

While the power stage uses an anode voltage which is relatively high, say 450 volts, the control electrodes thereof are biased negatively to a commensurately high value, say volts. This bias potential has heretofore been obtained by passing the steady component of the anode current of the push-pull stage through a resistor on its return path to the negative side 30 of the source J, and then utilizing the potential drop across the resistor for biasing the control electrodes of the power stage. I find that the energy consumed in this resistance is of the order of 6 watts, which is about the order of magnitude of the energy dissipated in the coil 24, despite the much higher terminal voltage diiference across the latter. In accordance with a further feature of my invention the energy which would otherwise be dissipated in obtaining the desired bias potential for the power stage is utilized for energizing the field of the reproducer H.

Referring to the wiring diagram, there is another field coil 42 which is connected in series with the lead 44 from the cathodes of the tubes in the power stage, so that the anode to cathode current of the power stage flows through the coil 42 on its return to the negative terminal of the source J. An audio frequency bypass condenser 46 is arranged in shunt with the coil 42 in order to provide a control electrode to cathode path for audio frequency energy in the power stage, and for the further purpose of shunting audio frequency components in the anode current away from the speaker field coil. It is obvious that the power stage G need not be a push-pull stage, and in such case the necessity for the condenser 46 is, of course, increased. With a push-pull stage the anode current is inherently steadied to a considerable extent, but it is nevertheless desirable to provide the condenser 46 in order to take care of the double audio frequency component which may otherwise be found present in the anode current lead. With coils 24 and 42 I find it is readily possible to dispense with the coil 41, but it is retained in the diagram for the purpose of illustration.

In the arrangement here set forth the speaker field is energized by the direct components of the anode currents of the amplifier and of the power stage, and such an arrangement is particularly desirable in practice because some 16 to 12 watts of energy are thus provided. Thus the speaker is energized entirely by normally wasted energy,

and sufilcient energy is provided to make possible economical construction of the speaker. However, it is clear that either type of field energization may be used alone, or may be used supplemented by energy fed directly from the same or the spirit of the invention, defined in the following claims.

I claim:

1. In the operation of an amplifier employing an electron emission tube having an anode, a

cathode, and a control electrode, the method of tential applied to the tube, the bias being made emission tube having an anode, a cathode, and

a control electrode, the method of normally controlling the output volume of the receiver which includes varying the magnitude of the direct potential applied to the anode of the tube and simultaneously and oppositely varying the strength of field energization of the reproducer.

4. In the operation of a radio receiver including a reproducer having an externally energized field, and an amplifier employing an electron emission tube having an anode, a cathode and a control electrode, the method of controlling the output volume of the receiver which includes varying the magnitude of the bias potential applied to the control electrode of the tube and simultaneously varying the strength of field energization of the reproducer in the same sense.

5. In the operation of a radio receiver including a reproducer having an externally energized field, and an amplifier employing an electron emission tube having an anode, a cathode, and a control electrode, the method of controlling the output volume of the receiver which includes varying the magnitude of the direct potential applied to the anode of the tube, and oppositely varying the magnitude of the bias potential applied to the control electrode of the tube and the strength of field energization of the reproducer.

6. An amplifier comprising an electron emission tube having an anode, a cathode, and a control electrode, and a single normally operated volume control therefor including means for varying the magnitude of the direct anode potential applied to the tube, and means for simultaneously and oppositely varying the magnitude of the control electrode bias potential applied to the tube, whereby the bias is made more negative when the anode is made less positive, and less negative when the anode is made more positive.

'7. A radio receiver comprising a reproducer having an externally energized field, an amplifier, and a normally operated volume control including means to vary the sensitivity of the amplifier, and means for simultaneously and oppositely varying the strength of field energize,- tion of the reproducer.

8. A radio receiver comprising a reproducer having an externally energized field, an amplifier employing an electron emission tube having an anode, a cathode, and a control electrode, and a normally operated volume control including means to vary the magnitude of the direct potential applied to the anode of the tube and means for simultaneously and oppositely varying the strength of field energization of the reproducer.

9. A radio receiver comprising a reproducer having an externally energized field, an amplifier employing an electron emission tube having an anode, a cathode, and a control electrode, and a volume control including means for varying the magnitude of the bias potential applied to the control electrode of the tube and means for simultaneously varying the strength of field energization of the reproducer in the same sense.

10. A radio receiver comprising a reproducer having an externally energized field, an amplifier employing an electron emission tube having an anode, a cathode, and a control electrode, and a volume control including means for varying the magnitude of the direct potential applied to the anode of the tube, means for simultaneously and. oppositely varying the magnitude of the bias potential applied to the control elec trode of the tube, and means for simultaneously and oppositely varying the strength of field energization of the reproducer.

11. A radio receiving system comprising an amplifier, an electro-dynamic reproducer having a field coil and an armature coil coupled to the system, a source of direct energy, means connecting the positive terminal of the source to the anodes of the amplifier through the field coil of the reproducer, means connecting the control electrodes 01 the amplifier to the negative terminal oi the source, means connecting the cathodes of the amplifier to the negative terminal of the source through biasing means, and a volume control circuit including a variable resistance normally operated to control the output volume of the system connected in series with the field coil and in shunt from the anode supply circuit of the amplifier to the negative terminal of the source in order to simultaneously and oppositely vary the anode potential of the amplifier and the strength of field energization of the reproducer.

12. A radio receiving system comprising an amplifier, a source of direct energy, means connecting the positive terminal of the source to the anodes of the amplifier through a fixed impedance, means connecting the control electrodes of the amplifier to the negative terminal of the source, means connecting the cathodes of the amplifier to the negative terminal of the source through a biasing resistor, and a volume control circuit including a variable resistance connected in shunt with the anode to cathode supply circuit of the amplifier in order to simultaneously vary the anode and control electrode potentials of the amplifier in an advantageous manner.

13. A radio receiving system comprising an amplifier, a source of direct energy, means connecting the positive terminal of the source to the anodes of the amplifier through a fixed impedance, means connecting the control electrodes of the amplifier to the negative terminal of the source, means connecting the cathodes of the amplifier to the negative terminal of the source through a biasing resistance, and a volume control 110 circuit including a series combination of a variable resistance and a fixed resistance connected in shunt with the anode to cathode supply circuit of the amplifier, said biasing and fixed resistances being so related as to produce cutoff in the ampli- 115 fier tubes when the variable resistance is reduced to zero.

14. A radio receiving system comprising an amplifier, a source of direct energy, means connecting the positive terminal of the source to the 120 anodes of the amplifier through a fixed impedance, means connecting the control electrodes of the amplifier to the negative terminal of the source, means connecting the cathodes of the amplifier to the negative terminal of the source 125 through a biasing resistance, and a volume control circuit including a series combination of a variable resistance and a fixed resistance connected in shunt with the anode to cathode supply circuit of the amplifier, said fixed resistance being 138 slightly smaller than the product of the bias resistance and the amplification constant of the amplifier tubes.

15. A radio receiving system comprising a radio frequency amplifier, an electro dynamic reproducer having a field coil and an armature coil coupled to the system, a source of direct en ergy, means connecting the positive terminal of the source to the anodes of the amplifier through the field coil of the reproducer, means connecting 1 the control electrodes of the amplifier to the negative terminal of the source, means connecting the cathodes of the amplifier to the negative terminal oi the source through a biasing resistor, i and a volume control circuit including a variable resistance connected in shunt with the anode to cathode supply circuit of the amplifier in order to simultaneously vary the anode and control electrode potentials of the amplifier and the strength 150 of field energization of the reprcducer in an advantageous manner.

16. A radio receiving system comprising a radio frequency amplifier, an audio frequency power stage, an electro dynamic reproducer having a pair of field coils, a source or" direct energy, means connecting the positive terminal of the source to the anode of the power stage, means connecting the control electrode of the power stage to the negative terminal of the source, means connecting the cathode of the power stage to the nega tive terminal of the source through one of the field coils of the reproducer, means connecting the positiveterminal of the source to the anodes of the amplifier through the other field coil of the reproducer, means connecting the control electrodes of the amplifier to the negative terminal of the source, and means connecting the cathodes of the amplifier to the negative terminal of the source through biasing means.

17. A radio receiving system comprising a radio frequency amplifier, an audio frequency power stage, an electro-dynamic reproducer having a pair of field coils, a source of direct energy, means connecting the positive terminal of the source to the anode of the power stage, means connect ing the control electrodes of the power stage to the negative terminal of the source, means con- 'necting the cathode of the power stage to the negative terminal of the source through one or the field coils of the reproducer, means connecting the positive terminal of the source to the anodes of the amplifier through the other field coil of the reproducer, means connecting the control electrodes" of the amplifier to the negative terminal of the source, means connecting the cathodes of the amplifier to the negative terminal of the source through biasing means, and a volume control circuit including a variable resistance connected in series with the second field coil and in shunt from the anode supply circuit of the amplifier to the negative terminal of the source in order to simultaneously and oppositely vary the anode potential of the amplifier and the strength of field energization of the reproducer.

18. A radio receiving system comprising a radio frequency amplifier, an audio frequency power stage, an electro-dynamic reproducer having a pair of field coils, a source of direct energy, means connecting the positive terminal of the source to the anode of the power stage, means connecting the control electrode of the power stage to the negative terminal of the source, means connecting the cathode of the power stage to the negative terminal of the source through one of the field coils of the reproducer, means connecting the positive terminal of the source to the anodes of the amplifier through the other field coil of the reproducer, means connecting the control elec- ,trodes of the amplifier to the negative terminal ,of the source, means connecting the cathodes of the amplifier to the negative terminal of the source through a biasing resistor, and a volume control circuit including a variable resistance connected in shunt with the anode to cathode supply circuit of the amplifier in order to simultaneously and automatically vary the anode and control electrode potentials of the amplifier and the strength of field energization of the reproducer.

19. In the operation of a radio receiver including an amplifier, a source of excess anode potential therefore, a reproducer having an externally energized field, and a volume control for varying the sensitivity of the amplifier, the method which includes utilizing the anode current fiowing from the source to the amplifier for energizing the field of the reproducer, utilizing additional auxiliary current from the source for further energizing the field of the reproducer, and simultaneously varying the sensitivity of the amplifier and the magnitude of the auxiliary current in opposite directions in order to keep up the field strength of the reproducer when the sensitivity of the amplifier is decreased.

20. A radio receiver comprising an amplifier, a source of excess anode potential therefor, a reproducer having externally energized field windings, a volume control for varying the sensitivity of the amplifier, means for feeding anode current from the source to the amplifier through the field windings, means for feeding additional auxiliary current from the source to the field windings, and means for varying the magnitude of the auxiliary current in a direction opposite to the variation of the sensitivity of the amplifier in order to keep up the field strength of the reproducer when the sensitivity of the amplifier is decreased.

21. In the operation of a radio receiver including an amplifier, a source of direct energy therefor, a reproducer having an externally energized field connected between the source and the amplifier, and a normally operated volume control for varying the sensitivity of the amplifier, the method which includes varying the sensitivity of the amplifier and simultaneously counteracting the change in field strength of the reproducer resulting from the change in anode current when the sensitivity of the amplifier is varied.

22. A radio receiver comprising an amplifier, a source of anode current therefor, a reprcducer having externally energized field windings, means for feeding the anode current from the source through the field windings, a normally operated volume control for varying the sensitivity of the amplifier, and means for counteracting the change in field strength of the reproducer resulting from the change in anode current when the sensitivity of the amplifier is varied.

23. In the operation of a radio receiver comprising an amplifier, a power stage, and an electro-dynamic reproducer having a plurality of independent field coils, the method of reducing the potential applied to the amplifier relative to that applied to the power stage, of biasing the control electrode of the power stage, and of energizing the field coil by otherwise wasted energy, which includes sending the direct current component of the anode to cathode current through a field coil of the reproducer and then to the amplifier, simultaneously and independently sending the direct current component of the anode to cathode current of the power stage first through the stage and then through another field coil of the reproducer, and biasing the power stage by applying thereto a difierence in potential obtained across the second field coil.

24. A radio receiver comprising a reproducer having a plurality of independent externally energizable field coils, a plurality of electron emis sion tubes having anodes, cathodes, and control electrodes, means for utilizing the steady component of the anode to cathode current of a tube for energizing one of the reproducer field coils and for biasing a tube by applying thereto a difference in potential obtained across the said field coil, and means for independently utilizing the steady component of the anode to cathode current of another tube for independently energizing another of the reproducer field coils and for reducing the anode potential applied to a tube by deducting therefrom a difference in potential obtained across the said latter field coil.

25. A radio receiver comprising an amplifier, a power stage, an electro-dynamic reproducer having a plurality of independent field coils, a source of direct energy, means for feeding the direct anode current for the amplifier first through a field coil of the reproducer in order to reduce the potential applied to the anodes of the tubes of the amplifier relative to that applied to the power stage, means for independently feeding the direct current component of the anode to cathode current of the power stage from the cathode through another field coil of the reproducer, and means to apply a difference in potential obtained thereacross to bias the power stage, whereby the field coils are energized entirely by otherwise wasted energy.

26. A radio receiver comprising an amplifier, a power stage, an electro-dynamic reproducer having a plurality of independent field coils, a rectifier, a multi-stage filter, means for feeding the direct anode current for the amplifier from the last stage of the filter through a field coil of the reproducer in order to reduce the potential applied to the anodes of the tubes of the amplifier relative to that applied to the power stage, means connecting the power stage anode to an intermediate stage of the filter in order to apply a relatively high potential thereto, means for independently feeding the direct current component of the anode to cathode current of the power stage from the cathode through another field coil of the reproducer, and means to apply a difference in potential obtained thereacross to bias the power stage.

27. A power operated radio receiver comprising a rectifier and multi-stage filter, a power stage, an amplifier requiring a lower anode potential than the power stage, a reproducer having an externally energizable field coil, means for feeding anode current from the last stage of the filter through the reproducer field coil to the amplifier in order to reduce the potential applied to the amplifier relative to that applied to the power stage and in order to energize the field coil, and means connecting the power stage to an intermediate stage of the filter in order to apply an increased anode potential thereto.

28. A power operated radio receiver comprising a source of direct current including a rectifier and multi-stage filter, a cascade amplifier,

a power stage, an electro-dynamic reproducer having a plurality of independent field coils, means for feeding direct current from the source to a field coil of the reproducer, means for feeding direct current from the last filter stage to the amplifier, means connecting the power stage anode to an intermediate stage of the filter in order to apply increased potential thereto, means for independently feeding the direct current component of the anode to cathode current of the power stage from the cathode through another field coil of the reproducer, and means to apply a difference in potential obtained thereacross as a biasing potential for the power stage.

29. A radio receiver comprising an amplifier, a power stage, an electro-dynamic reproducer having a plurality of independent field coils, a source of direct energy including rectifier and filter means, means for feeding filtered direct current from the source to one of the speaker coils, to the amplifier, and to the power stage, means for independently feeding the direct current component of the anode to cathode current of the power stage from the cathode through another field coil of the reproducer, and means to apply a difference in potential obtained thereacross to bias the power stage.

30. A radio receiver comprising a power stage, a source of anode potential including rectifier means and a filter having choke inductance and bypass condenser means, an amplifier requiring a lower anode potential than the power stage, a reproducer having an externally energizable field coil, means for feeding filtered anode current from the filter means directly to the power stage, and means for feeding filtered anode current from the filter means through the reproducer field coil to the amplifier in order to reduce the potential applied to the amplifier relative to that applied to the power stage, and in order to energize the field, said filtered anode current being the only current supplied to the aforesaid field coil, whereby the latter is energized entirely by otherwise wasted energy without producing hum.

31. A power operated radio receiver comprising a rectifier and multi-stage filter, a cascade amplifier, a. push-pull power stage, an electrodynamic reproducer having a plurality of independent field coils, means for feeding direct current from the last filter stage to a field coil of the reproducer and to the amplifier, means connecting the anodes of the power stage tubes to an intermediate stage of the filter in order to apply increased potential thereto, means for independently feeding the direct current components of the anode to cathode currents of the power stage tubes from the cathodes through another field coil of the reproducer, and means to apply a difference in potential obtained thereaoross to the grids of the power stage tubes in order to bias the same.

32. A radio receiver comprising an amplifier,

a push-pull power stage, an electro-dynamic reproducer having a plurality of independent field coils, a source of direct energy, means for feeding the direct anode current for the amplifier first through a field coil of the reproducer in order to reduce the potential applied to the anodes of the tubes of the amplifier relative to that applied to the power stage, means for independently feeding the direct current compolite nents of the anode to cathode currents of the 

